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Thread: To co-phase or not to co-phase

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    To co-phase or not to co-phase

    Was talking to a Hammie at his store today and he said it would be better off to run just one antenna and have the other as a dummy in case one of the cables get broken. Well if theyre ran together I guess both of them would be broke wouldnt they? Anyway, is it beneficial to run co-phase or is it better to run just one with a dummy? Theyre 4' top-loaded antennas. Thanks

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    In a way he's right...In order to get the full potential out of a co-phase set-up you need the antenna's spaced 9' apart...On a Big Rig truck that's possible, but not so much on something like a pick-up...Plus tuning just one antenna is allot less of a headache than tuning two antenna's.

    When the guy said to just run one antenna and have the other as a dummy antenna, what he's talking about is NOT using a co-phase harness, but to use just a single coax to the hot antenna...The other antenna (usually on the passenger side) would just be connected to the mirror bracket, with no coax connected to it...It would just be there for looks.

    Then if something happened to the drivers side antenna, you could always run a separate coax over to the passenger side...

    You can't use a co-phase coax to just one antenna...Co-phase coax is 75ohm, if you just have one side of a co-phase wiring harness hooked to one antenna and the other end not connected to a antenna your SWR will be sky-high...


  3. The Following User Says Thank You to JesseJamesDallas For This Useful Post:

    HankHill (02-04-2015)

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    Right, I figured that the antennas had to be spaced apart but wasnt sure by how much. And I am running these on a pick-up so theres no way they'll properly be 9' apart haha.

    Thank you very much!

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    Quote Originally Posted by HankHill View Post
    Right, I figured that the antennas had to be spaced apart but wasnt sure by how much. And I am running these on a pick-up so theres no way they'll properly be 9' apart haha.

    Thank you very much!
    You can still do it on a pick-up...It's just your not going to gain anything by having a co-phase set-up with the antenna's spaced less than 9' apart...


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    Even at 9 feet apart you won't notice the difference. If you really needed gain in two directions you really need 18 to 22 feet of separation.


    The DB

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    Quote Originally Posted by The DB View Post
    Even at 9 feet apart you won't notice the difference. If you really needed gain in two directions you really need 18 to 22 feet of separation.


    The DB
    Guess you could mount one antenna on the back bumper, and the second on the front bumper...That might work! I've seen stupider looking set-up's!


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    If you are going front to back, 4.5 feet between the antennas and feeding them 135 degrees out of phase (not perfectly in phase like "cophased" antennas) will net you descent gain in one direction with great rejection in the other. If you have more room you can spread them out some more as gain peaks at around 6 feet in this case, however, I doubt you would notice such a change in the real world...

    A friend of mine runs such a setup with 4.5 feet between the antennas on his suburban, he hears almost nothing from behind him, and I can talk to him from noticeably further away than others when he is facing me...


    The DB

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    Duel, co-phase, antennas became popular with truckers when Kenworth came out with the fiberglass roof. Not much of a ground plane. It is supposed to squish the pattern down the road to the front and to the rear. At an 8' spread it worked fine with 3 or 4 watts of a stock 1970's radio. When you increase the output (and I know you would never do that ) the extended squish kinda gets lost back into a pretty round pattern.

    I have always had co-phase and got out nicely. Meaning people come back to me when I talk (most of time). Lately I got into a Freightliner Columbia and had a shock when I found out that the truck is not wired for co-phase. The left antenna only goes to the CB and the right antenna only goes to the dash for the AM/FM/CD player.

    Being the first truck with a single antenna & a fiberglass cab, I talk all the time from the Southwest U.S. to Toronto, Quebec and New England quite often. I'm in no hurry to mount a co-phase system. On your pickup, if you mount your antenna dead center behind/or on the roof of the cab, you will have an oval pattern to the effect of more signal going down the highway than to the side anyway. I think if you have a little heat, the reason for having co-phase (as George Carlin put it) "Just Goes Away" haha

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